The present invention relates to an air float fixture support system for machine tool and other environments, and in particular to an automatic clamping system for clamping the fixture in place once it has been located on the air float table. Although the system is adapted for use in a variety of applications, it is most particularly suited for use in a machine tool environment wherein it is necessary to accurately locate and then clamp workpieces is a machining station.
The machining of large workpieces has often involved very difficult positioning and repositioning of the workpiece when the various portions thereof are machined. In many cases, it is necessary to use hoists for elevating and moving the workpiece about both to and from the machine tool table, and on the table itself where repositioning is necessary for sequential machining steps.
In order to overcome these problems, an air float system, wherein the workpiece is mounted to a fixture which in turn is supported on a film of pressurized air, has been developed. This system is described in detail in U.S. Pat. No. 4,058,885 in the name of Raymond A. Bergman, which patent is incorporated herein by reference. In the system, a table is provided with fluid passages and a plurality of fluid outlets distributed over the surface of the table so that a cushion of pressurized air may be provided underneath the workpiece fixture. By virtue of the fluid pressure film, substantially friction-free movement of the fixture on the table is possible thereby permitting positioning and repositioning to be accomplished by a single operator without the need for hoisting equipment.
In order for the fixture to be rotated and translated from one position to another, the table is provided with one or more retractable pivot pins which project upwardly from the table surface. The pins may either be received in a socket in the bottom of the fixture, in which case the fixture is constrained to move circularly on the table, or, alternatively, they may be received in one or more slots so that the fixture is not only rotatable but also translatable. Cooperating pairs of retractable pin and socket locating devices on the fixture and table provide for accurate location of the fixture in a variety of predetermined positions.
The table may be provided wth a dual centering pin feature if additional flexibility is desired in positioning and locating the fixture. The dual centering pin comprises an outer pin which is engagable with the fixture slots, and an inner pin received within the outer pin with means for causing the inner pin to extend upwardly out of the outer pin so as to engage holes in the slots. When the inner pin is retracted, the workpiece fixture is translatable on the table in engagement with the outer pin, and when the inner pin is extended and received within one of the fixture holes within the slots, the fixture may be rotated about it to the desired position.
In certain applications of air float systems of this type, as, for example, machine tool work tables, it is necessary to firmly clamp the workpiece supporting fixture in place during machining. Initially, conventional T-slots were provided in the upper surface of the air float table, and the slots were engaged by conventional T-clamps. The presence of T-slots on the surface of the table proved to be a problem, however, due to the loss of pneumatic pressure between the table and fixture. Subsequently, a bayonet clamping system was developed, which comprises a plurality of openings in the surface of the air float table engagable by lug-type or high pitch threaded pins which could be rapidly inserted and locked in place. Clamping pressure was transmitted to the fixture by means of conventional clamping bars, which were tightened down against the bayonet pins. By providing removable covers to close the unused female openings for the bayonet clamps, the problem of loss of pneumatic pressure was overcome. Such a system is described in pending U.S. No. 4,174,828 in the name of Raymond A Bergman.
One drawback to the bayonet clamping system is that manual insertion of the bayonet clamps by the machine tool operator is necessary. In the case of very large tables, it may be necessary for the operator to physically climb on the table in order to emplace the clamps. Furthermore, the clamps serve only to fix the pallet in place once it has been located, and play no role in the rough positioning of the fixture.